Massive absorber - Why is this technique not further pursued?

In the mid-1990s, a settlement was equipped with concrete absorbers. So-called energy stars or solid absorber plates were used on the garage roofs. The people I talked to are consistently very satisfied with them. I had the opportunity to speak with a person who was involved in the project at the time. The whole thing was sidelined by the then chairman of the Committee for Environment and Transport in the Baden-Württemberg state parliament, Kretschmann, with the words "You and your damn concrete" and the then low energy prices. Are there still providers of this technology? Why is this technology not being further pursued? There is hardly anything about it on Google. Perhaps someone has more information.

After all, it’s a heat pump whose heat source is a brine circulating in a ground-source heat exchanger embedded in concrete. The sun is supposed to shine on it (winter?). Whether this is nicer, cheaper, and more efficient than placing the collector in the ground or simply using air as a heat source via a fan... there were probably reasons against it, which is why it did not catch on. It probably has similar efficiency to an air-to-water heat pump but worse than ground. The heat capacity is likely limited because the concrete core is sluggish and cools down.